geology 117 -- the oceans get to web site from illinois compass instructor: prof. tom johnson...
TRANSCRIPT
GEOLOGY 117 -- THE OCEANS
Get to web site from Illinois Compass
Instructor: Prof. Tom [email protected]
•One set of notes for each class; linked to class One set of notes for each class; linked to class schedule on web pageschedule on web page
•Short reading assignments to be done Short reading assignments to be done beforebefore classes; listed in class schedule on web pageclasses; listed in class schedule on web page
•Get to the web page through CompassGet to the web page through Compass
Web Notes and ReadingsWeb Notes and Readings
What is Science?
•A collection of facts about nature?-It’s much more than that
•A process or method used to decide what is “true” and what is not?
-It is that, too.
•A collection of ideas dreamed up by scientists that keeps changing and is never really reliable?.....
Science is often reliable.
How science progresses, succeeds, and fails:
-We observe the world around us.
-We try to make sense of it all. If we succeed at that, then maybe we can predict what will happen, or find a way to make something useful.
-We make educated guesses- Hypotheses.
-Some don’t hold up – useless.
-Others do withstand the tests of time- useful!
-So we test them- BIG TIME
How science progresses, succeeds, and fails:
-Sometimes an idea becomes more than just an educated guess. After much testing, it really seems to work, and we call it a theory. Some theories are well established and reliable.
How science progresses, succeeds, and fails:
-Sometimes an idea becomes more than just an educated guess. After much testing, it really seems to work, and we call it a theory. Some theories are well established and reliable.
-Some theories are revised or overturned
-This does not mean that science is haphazard- it is part of the normal process
-We will examine the development of the theory of plate tectonics in this class.
Subdivisions of ocean science:Marine geologyChemical oceanographyPhysical oceanographyBiological oceanography
This is the basic order of topics in this course.
Class #2 -- Geology 117
The Earth, Part 1
•How did the Earth and Oceans form?How did the Earth and Oceans form?•What does the ocean floor look like (shape)?What does the ocean floor look like (shape)?•Why is it shaped that way?Why is it shaped that way?•Why does the earth have oceans and continents Why does the earth have oceans and continents instead of just a single shallow ocean covering instead of just a single shallow ocean covering everything?everything?•How do we “know” all this stuff anyway?How do we “know” all this stuff anyway?•Do we really “know” or is it more “inference” than Do we really “know” or is it more “inference” than knowledge?knowledge?
The Oceans- Part 1The Oceans- Part 1
Marine GeologyMarine Geology
Latitude lines are “parallels”: constant distance between
Latitude
Longitude (East-West)
Why measure longitude in degrees???
Continents mostly in the N hemisphere: Gives Earth a slight “pear” shape
About 5 B.Y. ago: Formation of the solar system Gravitational collapse, rotating disk… dust and gas (mostly H and He)
•Then… accretion -- planets.
•Earth, other planets, meteorites at ~ 4600 m.y.
•Early molten(?) stage of Earth (first 200 m.y.):
- silicate mantle and metallic core formed
When did the earth form and how did it form? How did it get
to be what it is today?
Layering of the Earth Based on
Chemical Composition
Layer Depth
(km)
State Comp. g/cm3 T˚C
Crust --
Continental
55
(25-90)
solid
(rigid)
"granite" 2.7 <1000
Crust --
Oceanic
10
(5-10)
solid
(rigid)
basalt 3.0 <1500
Mantle to 2900 solid
(ductile)
Mg, Fe
silicates
4.5 1500-
3000
Core-
Outer
2900-
5300
liquid Fe, Ni
metal
11.5 4000
Core-
Inner
5300-
6370
soild Fe, Ni
metal
13.0 5000
Fig. 1.14 in Text
What is the evidence for this?
• The way earthquake waves travel through• Each earthquake sends out waves• Thousands of seismographs detect these
– e.g., Earthquake in Turkey, detected here
• Two types of earthquake waves– compressional waves, or “P” waves– shear waves or “S” waves
P and S wave material not in textbook
http://www.eas.purdue.edu/~braile/edumod/waves/Pwave.htm
http://www.eas.purdue.edu/~braile/edumod/waves/Swave.htm
P- waves(refraction, shadow zone)
S- waves(blocked by liquid, large shadow zone
Homogeneous earth would be like this:
Homogeneous earth would be like this:
P and S wave material not in textbook
http://neic.usgs.gov/neis/eq_depot/2002/eq_021103/ak_seismic_waves.html
P- waves(refraction, shadow zone)
S- waves(blocked by liquid, large shadow zone
Homogeneous earth would be like this:
More evidence used to infer what’s inside the earth...
More evidence used to infer what’s inside the earth...
• Meteorites– Some are fragments of planets;
broken apart billions of years ago
– Some are Fe Metal
– Some are Mg+Fe silicates like the earth’s mantle
How do we know when all this happened (“age dates”)?
• Radioactive elements– Decay produces “daughter” products
• Some radioactive elements have very long half-lives (e.g., Uranium)
• Buildup of daughter products can be used to determine ages of rocks and meteorites
Represents amount of lead
Represents amount of uranium